Method for welding pipe pieces made of thermoplastics

Abstract

In a method for connecting pipe pieces of corrugated pipes to form a pipe, which is to be used in particular as a protection pipe for communication cables or light wave guides, external pipe segments are formed by appropriate cutting in the vicinity of the external pipe portions, which external pipe segments are inserted into recesses of welding sleeves. These welding sleeves comprise an outer ring and an inner ring, the inner ring not projecting radially beyond the inner pipe portions into the pipe. At least one of the rings is welded with the external pipe segments.

What is claimed is: 
     
       1. A method for welding together two pipe pieces of corrugated pipes comprising: providing a first thermoplastic pipe piece and a second thermoplastic pipe piece, each pipe comprising corrugated portions with internal pipe portions and external pipe portions alternately succeeding in the direction of a central longitudinal axis and with substantially radial flanks interconnecting the said two portions and said first pipe piece ending in a first front surface of a cylindrical external pipe segment, and said second pipe piece ending in a second front surface of a cylindrical external pipe segment,   providing a thermoplastic welding sleeve comprising an outer ring and an inner ring, which outer ring and which inner ring are arranged concentrically to said central longitudinal axis and which said outer ring and which said inner ring define a first annular recess and a second annular recess, which two recesses are separated by a middle web from each other, which middle web interconnects said outer ring and said inner ring, and wherein said inner ring radially to said central longitudinal axis is located exclusively between said external pipe segments and said internal pipe portions of said pipe pieces,   providing electrical heating elements adjacent to at least one of said outer ring and said inner ring,   pushing said external pipe segment of said first pipe piece into said first annular recess of said welding sleeve and said external pipe segment of said second pipe piece into said second annular recess of said welding sleeve,   plastifying at least one of said outer ring and said inner ring and said external pipe segments of said first and second pipe pieces by actuating the electric resistance heating elements with electric current,   pressing said two pipe pieces towards each other while deforming said external pipe segments until said external pipe segments fill at least substantially said two annular recesses and   switching off the electric current and cooling said welding sleeve and said external pipe segments to connect said external pipe segments with said welding sleeve.   
     
     
       2. A method according to claim 1, wherein said electric heating element consists of an electric resistant heating element arranged in said outer ring. 
     
     
       3. A method according to claim 1, wherein said electric heating element consists of an electric resistance heating element arranged in said inner ring. 
     
     
       4. A method according to claim 1, wherein said welding sleeve is provided with an inner ring which has a stiffening inlay. 
     
     
       5. A method according to claim 1, wherein an electric resistance heating element separated from the welding sleeve is provided, which electric resistance heating element is placed on said external pipe segments to be inserted into the respective recess. 
     
     
       6. A method according to claim 1, wherein said annular recesses slightly taper from front faces of said welding sleeve towards said middle web of said welding sleeve.